In a typical transaction, a consumer may drive a vehicle up to a fuel dispenser in a fueling environment. The consumer arranges for payment, either by paying at the pump, paying the cashier with cash, using a credit card or debit card, or some combination of these methods. The nozzle is inserted into the fill neck of the vehicle, and fuel is dispensed into the gas tank of the vehicle. Displays on the fuel dispenser display how much fuel has been dispensed as well as a dollar value associated with the fuel that has been dispensed. The customer relies on the fuel dispenser to accurately measure the amount of fuel dispensed and charge the customer accordingly. One method customers sometimes use to control costs is to pay for a preset amount of fuel based on a dollar or volume amount, called a “pre-pay.” Regulatory requirements, namely Weights & Measures, require that these customers receive all of the fuel for which they have paid to a highly accurate degree.
Operating behind the scenes of this process are valves that open and close the fuel flow path and a flow meter inside the fuel dispenser that measures the amount of fuel dispensed. The purpose of the flow meter is to measure accurately the amount of fuel being delivered to the customer's vehicle so that the customer may be billed accordingly and fuel inventory tracking may be undertaken. As noted, for preset dollar or volume transactions (pre-pays), the fuel dispenser relies on the flow meter to measure the fuel dispensed so as to know when to terminate the fuel flow.
Some fuel dispenser fuel flow meters are positive displacement meters, meaning that the actual displacement of the fuel is measured rather than measuring the flow rate and converting the flow rate into a volume. One example of an positive displacement meter that may be used is described in U.S. Pat. No. 5,447,062, entitled “Apparatus for measuring quantities of liquid in gasoline pumps of motor vehicle filling stations,” (hereinafter the “'062 patent”) incorporated herein by reference in its entirety. The '062 patent describes an axial meter that measures the displacement of a fluid by determining the number of rotations of axial spindles located inside the flow path of the meter.
As fluid enters the inlet port of the axial meter in the '062 patent, the fluid encounters two interlocked axial spindles, which causes the spindles to rotate. The outer edges of the spindles are located in close proximity to the internal housing of the meter, but they do not touch. Ball-bearings are provided on the shafts supporting the spindles to the housing of the meter so that the spindles can rotate freely. For every turn of the spindles, a given volume of fluid is displaced through the outlet of the meter. As the axial spindles rotate, a measuring transducer detects the rotation of the spindles so that the number of revolutions is known and can be electrically communicated to a control system and thus the volume of fluid displaced in also known.
A problem may occur when using a meter that relies on rotating components within to measure fluid like in the '062 patent. Using the example of the meter in the '062 patent, if the spindles lock-up meaning that they cannot rotate, such as would happen if debris blocked the spindles or the ball bearings failed, fluid would continue to flow around the edges of the spindles between the small gap between the outer edges of the spindles and the inner housing of the meter. The flow rate, however, would be reduced. A control system would not register fuel flow even though fuel is flowing, because the measuring transducer would not detect rotation of the spindles. In the example of the meter being used to measure fuel delivery from a fuel dispenser, it is not possible for a control system to detect the difference between no detection of rotation of the spindles due to the customer not squeezing the nozzle handle, and no detection of rotation of spindles due to a lock-up of the spindles preventing them from rotating. In the later instance, fuel is being delivered although not registered and not charged to the customer.
Therefore, a need exists for a control system to be able to distinguish between meter lock-up or other failure that prevent pulses indicative of flow to be generated by the meter, versus no request for delivery in the instance of no flow being detected by a measuring transducer or other measurement means to detect rotation of rotational components within a meter.